Altherr, 22, is 6-foot-5, 190 pounds. Brown, a left-handed hitter, is 6-foot-5, 205 pounds. Both are long and lean, with tremendous athletic ability and bodies that can generate both power and speed. Both play in the outfield.

I was able to scout them both in the Arizona Fall League. Brown in 2009, Altherr in '13.

At the young age of 22, Brown was given an early debut with the Major League club and scuffled a bit with the advanced pitching. Now, after more repetition, further development and greater experience seeing quality pitching, Brown is coming off a solid 2013 season. He made adjustments that helped bring out his natural hitting abilities. Altherr has similar challenges and similar ultimate potential.

Altherr's mother served in the armed forces and was stationed in Landstuhl, Germany. His father played professional German soccer.

The family moved to Avondale, Ariz., and Altherr graduated from Aqua Fria High School in 2009, where he played shortstop and pitched. He was then selected in the ninth round of the 2009 First-Year Player Draft by Philadelphia.

Altherr has completed parts of five seasons in the Phillies' Minor League system. He has a composite batting average of .260 covering 1,773 plate appearances. Altherr ranks 17th on the Phils' Top 20 Prospect list.

In Altherr's career until recently, hitting results had been inconsistent from year to year and from classification to classification. That said, his career was normal. Altherr was refining his swing, learning the game and experiencing better pitching as he went along. That's what happens with most prospects.

But the most encouraging sign of Altherr's development is best demonstrated in the 12 home runs he hit this past season at Class A Advanced Clearwater. He also had 36 doubles and six triples while stealing 23 bases in 28 attempts. It was a very solid season. Altherr flashed power and speed, the two tools that should bring him to prominence.

Not unlike what I saw early from Brown, Altherr has to do a better job recognizing breaking balls and offspeed pitches quickly. He then must determine his ability to hit the pitch. Sliders and curveballs challenged Altherr this past fall.

In Arizona, Altherr played in only 12 games. He hit .200 in 45 at-bats. Altherr had nine hits, including three doubles. He did not hit a triple or home run, but he stole two bases. He played errorless ball in the outfield.

Even with his long arms, Altherr's swing is fine. He doesn't try to do too much with the pitch. Rather, Altherr tries to meet the ball and make contact without adding length or aggression to his approach.

Ultimately, I believe Altherr's size will work more in his favor. He will be able to extend his arms and drive the ball with some loft. But again, Altherr has to recognize the pitch and adjust his swing and stride accordingly to fit his body.

For me, Altherr fits best in center field. He has the type of gliding long strides that can finish quickly on a ball in the air. Altherr sees the ball well off the bat and uses his speed and natural athletic ability to track the ball with sufficient range to take charge in the outfield. I also feel his arm strength is adequate for center but a bit light for right field.

Altherr is a work in progress. He is the type of hitter that can come quickly and make an impact. Altherr has outstanding upside as a natural athlete and is a potentially impactful hitter. His combination of size, raw power and speed from long strides will offer production in the Phillies' lineup. Just not yet.

Altherr is the type of athlete that excites scouts and player evaluators. He has the raw, unrefined potential of a game-changing player.

If he listens to instruction and learns to recognize and hit breaking balls, Altherr could easily become a fixture as a reliable center fielder. He's an exciting work in progress.

Bernie Pleskoff has served as a professional scout for the Houston Astros and Seattle Mariners. Follow @BerniePleskoff on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.